Execution sequence of finally and return

problem ： stay try-catch-finally In the code ,return and finally Who will execute first ？

Code 1 ：

 public static void main(String[] args) {
    
     int a = new ThreadPoolDemo().demo();
     System.out.println(a);
 }

 public int demo() {
    
     try {
    
         return 1;
     } finally {
    
         System.out.println("finally The module is executed ");
     }
 }

The operation results are as follows ：

finally The module is executed 
1

From the above operation results , In carrying out the return Run before finally Code , Why is that so ？ We can see the compiled code as follows ：

 public static void main(String[] args) {
    
     int a = (new PersonDemo()).demo();
     System.out.println(a);
 }

 public int demo() {
    
     byte var1;
     try {
    
         var1 = 1;
     } finally {
    
         System.out.println("finally  The module is executed ");
     }
     return var1;
 }

Found that after compiling return Optimized and put finally Back , Temporary variables are used in the middle var1 Stored , So naturally, the execution order is to output first finally And then execute return. meanwhile return It also means that this method is ready to exit after running .
Code 2 ：

public static void main(String[] args) {
    
    int a = new ThreadPoolDemo().demo();
    System.out.println(a);
}

public int demo() {
    
    try {
    
        int a = 1 / 0;
        return 1;
    } catch (Exception e) {
    
        System.out.println("catch  The code block is executed ");
        return 10;
    } finally {
    
        System.out.println("finally  The module is executed ");
    }
}

The operation results are as follows ：

catch  The code block is executed 
finally  The module is executed 
10

Why is this output , Let's look at the compiled code as follows ：

public static void main(String[] args) {
    
    int a = (new PersonDemo()).demo();
    System.out.println(a);
}

public int demo() {
    
    byte var2;
    try {
    
        int a = 1 / 0;
        var2 = 1;
        return var2;
    } catch (Exception var6) {
    
        System.out.println("catch  The code block is executed ");
        var2 = 10;
    } finally {
    
        System.out.println("finally  The module is executed ");
    }

    return var2;
}

Or because the code is automatically optimized .

Code three ：

public class PersonDemo {
    

    public static void main(String[] args) {
    
        int a = new PersonDemo().demo();
        System.out.println(a);
    }

    public int demo() {
    
        try {
    
            int a = 1 / 0;
            return 1;
        } catch (Exception e) {
    
            System.out.println("catch  The code block is executed ");
            return 10;
        } finally {
    
            System.out.println("finally  The module is executed ");
            return 20;
        }
    }
}

The running results are as follows ：

catch  The code block is executed 
finally  The module is executed 
20

After reading the running results, let's look at the compiled code as follows ：

 public static void main(String[] args) {
    
     int a = (new PersonDemo()).demo();
     System.out.println(a);
 }

 public int demo() {
    
     try {
    
         boolean var2;
         try {
    
             int a = 1 / 0;
             var2 = true;
         } catch (Exception var6) {
    
             System.out.println("catch  The code block is executed ");
             var2 = true;
         }
     } finally {
    
         System.out.println("finally  The module is executed ");
         return 20;
     }
 }

It can be seen from here that as long as finally Code terminator is added in return, Other places return All ignored , stay finally To add return It's equivalent to adding return The effect is the same , Look at the code below , Let it not run abnormally ：

 public static void main(String[] args) {
    
     int a = new PersonDemo().demo();
     System.out.println(a);
 }

 public int demo() {
    
     try {
    
         return 1;
     } catch (Exception e) {
    
         System.out.println("catch  The code block is executed ");
         return 10;
     } finally {
    
         System.out.println("finally  The module is executed ");
         return 20;
     }
 }

The operation results are as follows ：

finally  The module is executed 
20

The compiled code looks like this ：

 public static void main(String[] args) {
    
     int a = (new PersonDemo()).demo();
     System.out.println(a);
 }

 public int demo() {
    
     try {
    
         boolean var1 = true;
     } catch (Exception var6) {
    
         System.out.println("catch  The code block is executed ");
         boolean var2 = true;
     } finally {
    
         System.out.println("finally  The module is executed ");
         return 20;
     }
 }

Find that as long as finally Add return, Finally, the return value of this method can only be finally Return value in .